Without limiting the scope of the invention, its background is described in connection with perforating oil wells to allow for hydrocarbon production, as an example. Shaped charges are typically used to make hydraulic communication passages, called perforations, in a wellbore drilled into the earth. The perforations are needed as casing is typically cemented in place with the wellbore. The cemented casing hydraulically isolates the various formations penetrated by the wellbore.
Shaped charges typically include a housing, a quantity of high explosive and a liner. The liner has a generally conical shape and is formed by compressing powdered metal. The major constituent of the powdered metal was typically copper. The powdered copper was typically mixed with a fractional amount of lead, for example twenty percent by weight, and trace amount of graphite as a lubricant and oil to reduce oxidation.
In operation, the perforation is made by detonating the high explosive which causes the liner to collapse. The collapsed liner or jet is ejected from the shaped charge at very high velocity. The jet is able to penetrate the casing, the cement and the formation, thereby forming a perforation.
The penetration depth of the perforation into the formation is highly dependent upon the design of the shaped charge. For example, the penetration depth may be increased by increasing the quantity of high explosive which is detonated to propel the jet. It has been found, however, that increasing the quantity of explosive not only increase penetration depth but may also increase the amount of collateral damage to the wellbore and to equipment used to transport the shaped charge to depth.
Attempts have been made to design a liner using a powdered metal having a higher density than copper. For example, attempts have been made to design a liner using a mixture of powdered tungsten, powdered copper and powdered lead. This mixture yields a higher penetration depth than typical copper-lead liners. Typical percentages of such a mixture might be 55% tungsten, 30% copper and 15% lead. It has been found, however, the even greater penetration depths beyond that of the tungsten-copper-lead mixture are desirable.
Therefore a need has arisen for a shaped charge that yields improved penetration depths when used for perforating a wellbore. A need has also arisen for such a shaped charge having a liner that utilizes a high performance powdered metal mixture to achieve improved penetration depths.